A food safety group filed a lawsuit in hopes of forcing the U.S. Department of Agriculture to release documents in court that could explain why the federal agency approved genetically engineered alfalfa despite its misgivings about environmental safety.

The Washington-based Center for Food Safety said Thursday the USDA may have come under pressure by seed giant Monsanto Co. to grant approval of its Roundup Ready alfalfa, which is designed to withstand multiple applications of herbicide.

“USDA determined Monsanto’s Roundup Ready alfalfa posed significant environmental and economic harms and initially proposed placing restrictions on it. Yet the agency went ahead and granted full unrestricted approval one month later,” Andrew Kimbrell, executive director for the Center for Food Safety, said in a prepared statement. “Did the White House intervene? Did Monsanto pressure the agency? The fact is we don’t know, and unless the court orders USDA to hand over these documents we may never know.”

[Updated 2:50 p.m.]

In an e-mailed statement, Monsanto dismissed the Center for Food Safety's characterization of the biotech alfalfa.

"Many thousands of farmers across the U.S. currently grow Roundup Ready alfalfa, corn, soybeans, cotton, sugar beets and canola," the company said. "Each of these crops was subjected to thorough scientific review by three separate federal agencies before reaching the market; none presents the types of risks CFS alleges."

The USDA did not reply to a request for comment.

Alfalfa is the fourth most commonly grown crop in the U.S. behind corn, soybeans and wheat. The legume is a key feed for dairy cows and a major ingredient in dietary supplements and herbal medicines. The U.S. is also a major exporter of alfalfa.

Opposition to genetically modified alfalfa centers on fears that it could contaminate traditional alfalfa fields since the crop is pollinated by bees. That could hurt organic farmers or exporters to countries where GMO is restricted. The USDA echoed some of those concerns in analysis presented in court several years ago.

But in 2011 the agency granted unrestricted commercial cultivation of the crop.

The Center for Food Safety said it hopes to obtain 1,179 documents from the USDA that could shed light on how it made its decision. The group said it has tried unsuccessfully to garner the documents through the Freedom of Information Act.

Roundup Ready alfalfa was developed by Monsanto and Forage Genetics, an alfalfa seed maker owned by Land O’Lakes Inc.

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